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Tuesday, February 11, 2014

What goes around, comes around On September 3, 2002, an amateur astronomer named Bill Yeung looked ...

What goes around, comes around

On September 3, 2002, an amateur astronomer named Bill Yeung looked into his telescope and discovered a strange object near Earth. Experts were surprised to discover that it was orbiting Earth! The orbit was unstable, which meant this object hadn't been here long. But there was no recently launched spacecraft that matched the orbit of this thing!

It got the name J002E3. It's fun to watch this animated gif and see how J002E3 came in from the Lagrange point L1 between the Earth and Sun, went around the Earth a few times, and then got kicked out.

But what was it?

University of Arizona astronomers found that its electromagnetic spectrum was consistent with white titanium dioxide paint - the same paint used by NASA for the Saturn V rockets. Tracing back its orbit, they found that it had probably been orbiting the Sun for 31 years. The last time it was near Earth was1971.

This seemed to suggest that it was a part of the Apollo 14 mission. But NASA knew the whereabouts of all hardware used for this mission! The third stage of that rocket, for example, was deliberately crashed into the Moon for seismic studies.

So, the most likely explanation seems to be that J002E3 is the third stage of the rocket for Apollo 12. NASA originally planned to shoot this into an orbit around the Sun. But they used more of the propellant than planned, and it seems that venting the rest didn't give this rocket stage enough energy to escape the Earth–Moon system. So, it ended up in a complicated orbit around the Earth after passing by the Moon on November 18, 1969.

It may hit earth someday! It weighs 10 tonnes. But don't worry: a 10-tonne meteor hits the Earth every few years, and most of them don't cause much trouble.

I think saw this animated gif in a post by Ole Olson. The explanation here is adapted from Wikipedia: